Ionic/Electronic Thermopower and Oxygen Thermotransport of Undoped La2NiO4+δ

Abstract

As technology develops to its cutting edge, environmental issue has emerged due to massive use of fossil fuel. To successfully cope with the global environmental problems, generating renewable green energy using Solid Oxide Fuel Cell is suggested as a pertinent alternative. Mixed Ionic Electronic Conductors (MIECs) are promising materials used in Solid Oxide Fuel Cell. In this context, mass/charge transport properties of MIECs are studied in order to understand their properties thoroughly. As materials that are used in forming solid-state device and is utilized in pumping/separation application, MIEC has recognized its importance. In this study, La2NiO4+δ is used as a targeted MIEC because it has high ionic and electronic transport properties. Along with these properties, mass/charge transport properties under isothermal condition have been explored. Despite these efforts, mass/charge transport properties under non-isothermal condition have not been navigated thoroughly. Throughout this work, mass/charge transport properties of this system under non-isothermal condition have measured by using two-probe ion blocking technique. By using this technique, ionic/electronic thermopowers are obtained and oxygen thermotransport of undoped La2NiO4+δ has been studied. For this oxide system, ionic thermopowers are measured. With previously studied isothermal transport properties, 2x3 Onsager matrix is completed. Experiment of undoped La2NiO4+δ is performed in temperature range of 800 ~ 1000ºC as a function of ˗6<logao2<0. Under these thermodynamic conditions, transient ionic thermopower and ionic/electronic thermopowers under Soret condition are measured. By using ionic/electronic thermopowers under Soret condition, non-isothermal transport coefficients are calculated. According to the nonisothermal transport coefficients, oxygen ion and hole appeared to be moving from relatively hotter side to colder side. Also, the effect of temperature difference to oxygen activity difference is calculated. When the temperature difference is about 100K, the effect to oxygen activity is approximately ΔlogaO2 ~ 1.5. Also, term reduced heat of transport of oxygen, which gives insight to oxygen ion movement based on heat, is evaluated. Values of reduced heat of transport vary from -200 to 100 kJ/mole. At last, chemical potential variation from upper and bottom of specimen is studied in order to obtain deeper understanding of oxygen thermotransport.